1. Field of the Invention
The invention pertains to compositions of matter, phase change inks and methods of reducing coefficients of friction associated with the surfaces of printed phase change inks.
2. Description of the Relevant Art
In general, phase change inks are in a solid phase at ambient temperature, but exist in a liquid phase at an elevated operating temperature of an ink jet printing device. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of a printing media, they solidify to form a printed pattern. Phase change ink methodology is described generally in U.S. Pat. Nos. 4,889,560; 5,372,852 and 5,827,918, all of which are assigned to the assignee of the present invention and incorporated herein by reference.
Phase change inks typically comprise a tetra-amide, a tackifier, and a viscosity modifying agent as primary components. An exemplary viscosity modifying agent is stearylstearamide, which can be provided to a concentration of less than or equal to about 50% (by weight) in a phase change ink.
Exemplary tackifiers are: KE-311 Resin, a glycerol ester of hydrogenated abietic (rosin) acid made by Arakawa Chemical Industries Ltd.; and KE-100 Resin, an ester of tetrahydroabietic acid and glycerol, which is also available from Arakawa Chemical Industries Ltd. Tackifiers are typically provided to a concentration of less than or equal to about 25% (by weight) in a phase change ink.
Exemplary tetra-amide compounds can be formed by reacting ethylene diamine with a dimer acid and an appropriate fatty acid. Various tetra-amide compounds are described in U.S. Pat. Nos. 4,830,671 and 5,194,638. Such exemplary compounds comprise the general formula ##STR2##
wherein R.sub.1 comprises a polymerized fatty acid residue, R.sub.2 and R.sub.3 represent groups with up to 12 carbon atoms, and R.sub.4 and R.sub.5 represent groups with up to 36 carbon atoms. The tetra-amide compounds of phase change inks are typically provided in the inks to from about 15% to about 35% (by weight) to increase glass transition temperature (T.sub.g) and adhesion. Tetra-amide compounds can further provide hardness, dye solubility, thermal stability and toughness to a phase change ink.
In addition to the above-described primary components, phase change inks can comprise a number of secondary components such as, for example, dyes, plasticizers, and antioxidants, as described in, for example, U.S. Pat. Nos. 4,889,560 and 5,372,852.
A printed phase change ink can have a waxy surface texture. A difficulty in utilizing phase change inks can be that the waxy textured surface will have a relatively high coefficient of friction when slid over a glass surface. Such can cause inconveniences when photocopying or scanning an image formed with phase change inks. For instance, when a printed image is placed on a glass surface of a photocopier, the waxy surface of the printed phase change ink can stick to the glass surface of the copier and cause smudges, and possibly even jam the copier. It is therefore desirable to develop new phase change ink compositions having lower coefficients of friction than presently available compositions.
A method which has been utilized with some success to reduce the coefficient of friction of printed ink surfaces is to incorporate polyethylene wax into phase change inks. Unfortunately, it is found that polyethylene waxes are of limited solubility in present phase change ink formulations. It would be desirable to develop new ink formulations having improved solubility of polyethylene waxes.